Devices and methods for exposure of printed circuit board substrates to a gaseous plasma (generally defined as gaseous matter in an elevated state, and more specifically for purposes of this application defined as gas molecules excited by exposure to an electrical field thereby forming ions and free radicals) for enhancing board quality by improving one or more of etching, cleaning and activation of substrates, desmearing of openings, or holes, through the circuit board, conductive surface oxide removal and the like have been heretofore suggested and/or utilized. Known devices have included devices and methods employing a chamber, a vacuum pump, a source of RF energy and metered gases (as is well known in the art). Such devices, however, have not proved completely effective in providing uniform plasma treatment of all areas of the circuit boards, and particularly including openings provided through the circuit board.
Devices and methods have been suggested and/or utilized for improving the uniformity of plasma treatment of printed circuit boards, including multilayered printed circuit boards. Such devices have included arrangements for improving the flow of plasma through the holes in the circuit boards, by, for example, reversing the flow of plasma and/or providing a plurality of electrode pairs supplied with varying quantities of electrical energy to compensate for saturation of plasma gases as the plasma flows from one end of the chamber to the other (see U.S. Pat. Nos. 4,328,081 and 4,425,210).
While some such devices as have heretofore been suggested and/or utilized have improved uniformity of plasma treatment of printed circuit boards, further improvements could nevertheless still be utilized.